Information About Configuring IEEE 802.3ad Link Bundling

Gigabit EtherChannel

Gigabit EtherChannel (GEC) is high-performance Ethernet technology that provides Gigabit per second (Gb/s) transmission rates. A Gigabit EtherChannel bundles individual Ethernet links (Gigabit Ethernet or Ten Gigabit Ethernet) into a single logical link that provides the aggregate bandwidth of up to four physical links. All LAN ports in each EtherChannel must be the same speed and all must be configured as either Layer 2 or Layer 3 LAN ports. Inbound broadcast and multicast packets on one link in an EtherChannel are blocked from returning on any other link in the EtherChannel.

When a link within an EtherChannel fails, traffic previously carried over the failed link switches to the remaining links within that EtherChannel. Also when a failure occurs, a trap is sent that identifies the device, the EtherChannel, and the failed link.

Port-Channel and LACP-Enabled Interfaces

Each EtherChannel has a numbered port-channel interface that must be manually created before interfaces can be added to the channel group. The configuration of a port-channel interface affects all LAN ports assigned to that port-channel interface.

To change the parameters of all ports in an EtherChannel, change the configuration of the port-channel interface; for example, if you want to configure Spanning Tree Protocol or configure a Layer 2 EtherChannel as a trunk. Any configuration or attribute changes you make to the port-channel interface are propagated to all interfaces within the same channel group as the port-channel; that is, configuration changes are propagated to the physical interfaces that are not part of the port-channel but are part of the channel group.

The configuration of a LAN port affects only that LAN port.

IEEE 802.3ad Link Bundling

The IEEE 802.3ad Link Bundling feature provides a method for aggregating multiple Ethernet links into a single logical channel based on the IEEE 802.3ad standard. This feature helps improve the cost effectiveness of a device by increasing cumulative bandwidth without necessarily requiring hardware upgrades. In addition, IEEE 802.3ad Link Bundling provides a capability to dynamically provision, manage, and monitor various aggregated links and enables interoperability between various Cisco devices and devices of third-party vendors.

LACP supports the automatic creation of EtherChannels by exchanging LACP packets between LAN ports. LACP packets are exchanged only between ports in passive and active modes. The protocol “learns” the capabilities of LAN port groups dynamically and informs the other LAN ports. After LACP identifies correctly matched Ethernet links, it facilitates grouping the links into an EtherChannel. Then the EtherChannel is added to the spanning tree as a single bridge port.

Both the passive and active modes allow LACP to negotiate between LAN ports to determine if they can form an EtherChannel, based on criteria such as port speed and trunking state. (Layer 2 EtherChannels also use VLAN numbers.) LAN ports can form an EtherChannel when they are in compatible LACP modes, as in the following examples:

A LAN port in active mode can form an EtherChannel with another LAN port that is in active mode.

A LAN port in active mode can form an EtherChannel with another LAN port in passive mode.

A LAN port in passive mode cannot form an EtherChannel with another LAN port that is also in passive mode because neither port will initiate negotiation.

LACP uses the following parameters:

LACP system priority—You must configure an LACP system priority on each device running LACP. The system priority can be configured automatically or through the command-line interface (CLI). LACP uses the system priority with the device MAC address to form the system ID and also during negotiation with other systems.

LACP port priority—You must configure an LACP port priority on each port configured to use LACP. The port priority can be configured automatically or through the CLI. LACP uses the port priority to decide which ports should be put in standby mode when there is a hardware limitation that prevents all compatible ports from aggregating. LACP also uses the port priority with the port number to form the port identifier.

LACP administrative key—LACP automatically configures an administrative key value on each port configured to use LACP. The administrative key defines the ability of a port to aggregate with other ports. A port’s ability to aggregate with other ports is determined by the following:

On ports configured to use LACP, it tries to configure the maximum number of compatible ports in an EtherChannel, up to the maximum allowed by the hardware. To use the hot standby feature in the event a channel port fails, both ends of the LACP bundle must support the
lacpmax-bundle command.

As a control protocol, LACP uses the Slow Protocol Multicast address of 01-80-C2-00-00-02 to transmit LACP protocol data units (PDUs). Aside from LACP, the Slow Protocol linktype is to be utilized by operations, administration, and maintenance (OAM) packets, too. Subsequently, a subtype field is defined per the IEEE 802.3ad standard [1] (Annex 43B, section 4) differentiating LACP PDUs from OAM PDUs.

Note

LACP and Port Aggregation Control Protocol (PAgP) are not compatible. Ports configured for PAgP cannot form port channels on ports configured for LACP, and ports configured for LACP cannot form port channels on ports configured for PAgP.

Link failover time of 250 milliseconds or less and a maximum link failover time of 2 seconds; port channels remain in the LINK_UP state to eliminate reconvergence by the Spanning-Tree Protocol.

Shutting down a port channel when the number of active links falls below the minimum threshold. In the port channel interface, a configurable option is provided to bring down the port channel interface when the number of active links falls below the minimum threshold. For the port-channel state to be symmetric on both sides of the channel, the peer must also be running LACP and have the same
lacpmin-bundle command setting.

The IEEE Link Aggregation Group (LAG) MIB.

LACP for Gigabit Interfaces

The LACP (802.3ad) for Gigabit Interfaces feature bundles individual Ethernet links (Gigabit Ethernet or Ten Gigabit Ethernet) into a single logical link that provides the aggregate bandwidth of up to four physical links.

All LAN ports on a port channel must be the same speed and must all be configured as either Layer 2 or Layer 3 LAN ports. If a segment within a port channel fails, traffic previously carried over the failed link switches to the remaining segments within the port channel. Inbound broadcast and multicast packets on one segment in a port channel are blocked from returning on any other segment of the port channel.

Note

The network device may impose its own limits on the number of bundled ports per port channel.

Guidelines for LACP for Gigabit Interfaces Configuration

Port channel interfaces that are configured improperly with LACP are disabled automatically to avoid network loops and other problems. To avoid configuration problems, observe these guidelines and restrictions:

Every port added to a port channel must be configured identically. No individual differences in configuration are allowed.

Bundled ports can be configured on different line cards in a chassis.

Maximum transmission units (MTUs) must be configured on only port channel interfaces; MTUs are propagated to the bundled ports.

QoS and committed access rate (CAR) are applied at the port level. Access control lists (ACLs) are applied on port channels.

MAC configuration is allowed only on port channels.

MPLS IP should be enabled on bundled ports using the
mplsip command.

Unicast Reverse Path Forwarding (uRPF) should be applied on the port channel interface using the
ipverifyunicastreverse-path command in interface configuration mode.

Cisco Discovery Protocol should be enabled on the port channel interface using the
cdpenable command in interface configuration mode.

All LAN ports in a port channel should be enabled. If you shut down a LAN port in a port channel, the shutdown is treated as a link failure and the traffic is transferred to one of the remaining ports in the port channel.

Create a port channel interface using the
interfaceport-channel command in global configuration mode.

When an Ethernet interface has an IP address assigned, disable that IP address before adding the interface to the port channel. To disable an existing IP address, use the
noipaddress command in interface configuration mode.

The
holdqueuein command is valid only on port channel interfaces. The
holdqueueout command is valid only on bundled ports.

active—Places a port into an active negotiating state, in which the port initiates negotiations with other ports by sending LACP packets.

passive—Places a port into a passive negotiating state, in which the port responds to LACP packets it receives but does not initiate LACP negotiation. In this mode, the channel group attaches the interface to the bundle.

Step 8

exit

Example:

Device(config-if)# exit

Returns to global configuration mode.

Step 9

interfacetypeslot/subslot// port

Example:

Device(config)# interface gigabitethernet 4/0/0

Specifies the next port to bundle and places the CLI in interface configuration mode.

Step 10

noipaddress

Example:

Device(config-if)# no ip address

Disables the IP address on the port channel interface.

Step 11

channel-groupchannel-group-numbermode {active |
passive}

Example:

Device(config-if)# channel-group 1 mode active

Assigns the interface to the previously configured port channel group.

channel-group-number—Valid range is 1 to 64.

active—Places a port into an active negotiating state, in which the port initiates negotiations with other ports by sending LACP packets.

passive—Places a port into a passive negotiating state, in which the port responds to LACP packets it receives but does not initiate LACP negotiation. In this mode, the channel-group attaches the interface to the bundle.

Setting LACP System Priority and Port Priority

Perform this task to set the LACP system priority and port priority. The system ID is the combination of the LACP system priority and the MAC address of a device. The port identifier is the combination of the port priority and port number.

SUMMARY STEPS

1.enable

2.configureterminal

3.lacpsystem-prioritypriority

4.interfaceslot/subslot// port

5.lacpport-prioritypriority

6.end

7.showlacpsys-id

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Device> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2

configureterminal

Example:

Device# configure terminal

Enters global configuration mode.

Step 3

lacpsystem-prioritypriority

Example:

Device(config)# lacp system-priority 200

Sets the system priority.

Step 4

interfaceslot/subslot// port

Example:

Device(config)# interface gigabitethernet 0/1/1

Specifies the bundled port on which to set the LACP port priority and enters interface configuration mode.

Step 5

lacpport-prioritypriority

Example:

Device(config-if)# lacp port-priority 500

Specifies the priority for the physical interface.

priority—Valid range is from 1 to 65535. The higher the number, the lower the priority.

Step 6

end

Example:

Device(config-if)# end

Returns to privileged EXEC mode.

Step 7

showlacpsys-id

Example:

Device# show lacp 200

Displays the system ID (a combination of the system priority and the MAC address of the device).

Troubleshooting Tips

To verify and isolate a fault, start at the highest level maintenance domain and do the following:

Check the device error status.

When a error exists, perform a loopback test to confirm the error.

Run a traceroute to the destination to isolate the fault.

If the fault is identified, correct the fault.

If the fault is not identified, go to the next lower maintenance domain and repeat steps 1 through 4 at that maintenance domain level.

Repeat the first four steps, as needed, to identify and correct the fault.

Displaying Gigabit EtherChannel Information

To display Gigabit Ethernet port channel information, use the
showinterfacesport-channel command in user EXEC mode or privileged EXEC mode. The following example shows information about port channels configured on ports 0/2 and 0/3. The default MTU is set to 1500 bytes.

The table below describes the significant fields shown in the display.

Table 2
showinterfacesport-channel Field Descriptions

Field

Description

Port-channel1 is up, line protocol is up

Indicates the bundle interface is currently active and can transmit and receive or it has been taken down by an administrator.

Hardware is

Hardware type (Gigabit EtherChannel).

address is

Address being used by the interface.

MTU

Maximum transmission unit of the interface.

BW

Bandwidth of the interface, in kilobits per second.

DLY

Delay of the interface, in microseconds.

reliability

Reliability of the interface as a fraction of 255 (255/255 is 100 percent reliability), calculated as an exponential average over 5 minutes.

tx load rxload

Transmit and receive load on the interface as a fraction of 255 (255/255 is completely saturated), calculated as an exponential average over 5 minutes. The calculation uses the value from the
bandwidth interface configuration command.

Encapsulation

Encapsulation type assigned to the interface.

loopback

Indicates if loopbacks are set.

keepalive

Indicates if keepalives are set.

ARP type

Address Resolution Protocol (ARP) type on the interface.

ARP Timeout

Number of hours, minutes, and seconds an ARP cache entry stays in the cache.

No. of active members in this channel

Number of bundled ports (members) currently active and part of the port channel group.

Member <no.> Gigabit Ethernet: <no. /no. /no. >

Number of the bundled port and associated Gigabit Ethernet port channel interface.

Last input

Number of hours, minutes, and seconds since the last packet was successfully received by an interface and processed locally on the Device. Useful for knowing when a dead interface failed. This counter is updated only when packets are process-switched, not when packets are fast-switched.

output

Number of hours, minutes, and seconds since the last packet was successfully transmitted by an interface. This counter is updated only when packets are process-switched, not when packets are fast-switched.

output hang

Number of hours, minutes, and seconds since the interface was last reset because of a transmission that took too long. When the number of hours in any of the “last” fields exceeds 24 hours, the number of days and hours is printed. If that field overflows, asterisks are printed.

last clearing

Time at which the counters that measure cumulative statistics (such as number of bytes transmitted and received) shown in this report were last reset to zero. Variables that might affect routing (for example, load and reliability) are not cleared when the counters are cleared.

*** indicates that the elapsed time is too long to be displayed.

0:00:00 indicates that the counters were cleared more than 231 ms and less than 232 ms ago.

Input queue

Number of packets in the input queue and the maximum size of the queue.

Number of packets in the output queue and the maximum size of the queue.

5 minute input rate 5 minute output rate

Average number of bits and packets received or transmitted per second in the last 5 minutes.

packets input

Total number of error-free packets received by the system.

bytes (input)

Total number of bytes, including data and MAC encapsulation, in the error-free packets received by the system.

no buffer

Number of received packets discarded because there was no buffer space in the main system. Broadcast storms on Ethernet lines and bursts of noise on serial lines are often responsible for no input buffer events.

broadcasts

Total number of broadcast or multicast packets received by the interface.

runts

Number of packets that are discarded because they are smaller than the minimum packet size for the medium.

giants

Number of packets that are discarded because they exceed the maximum packet size for the medium.

input errors

Total number of no buffer, runts, giants, cyclic redundancy checks (CRCs), frame, overrun, ignored, and abort counts. Other input-related errors can also increment the count, so that this sum might not balance with the other counts.

CRC

CRC generated by the originating LAN station or far-end device does not match the checksum calculated from the data received. On a LAN, this usually indicates noise or transmission problems on the LAN interface or the LAN bus. A high number of CRCs is usually the result of collisions or a station transmitting bad data. On a serial link, CRCs usually indicate noise, gain hits or other transmission problems on the data link.

frame

Number of packets received incorrectly having a CRC error and a noninteger number of octets. On a serial line, this is usually the result of noise or other transmission problems.

overrun

Number of times the serial receiver hardware was unable to pass received data to a hardware buffer because the input rate exceeded the receiver’s capacity for handling the data.

ignored

Number of received packets ignored by the interface because the interface hardware ran low on internal buffers. These buffers are different than the system buffers mentioned previously in the buffer description. Broadcast storms and bursts of noise can cause the ignored count to be incremented.

watchdog

Number of times the watchdog receive timer expired.

multicast

Number of multicast packets received.

packets output

Total number of messages transmitted by the system.

bytes (output)

Total number of bytes, including data and MAC encapsulation, transmitted by the system.

underruns

Number of times that the far-end transmitter has been running faster than the near-end Device’s receiver can handle.

output errors

Sum of all errors that prevented the final transmission of datagrams out of the interface being examined. Note that this might not balance with the sum of the enumerated output errors, as some datagrams can have more than one error, and others can have errors that do not fall into any of the specifically tabulated categories.

collisions

Number of messages retransmitted because of an Ethernet collision. A packet that collides is counted only once in output packets.

interface resets

Number of times an interface has been completely reset. This can happen if packets queued for transmission were not sent within a certain interval. If the system notices that the carrier detect line of an interface is up but the line protocol is down, the system periodically resets the interface in an effort to restart that interface. Interface resets can also occur when an unrecoverable interface processor error occurred, or when an interface is looped back or shut down.

babbles

The transmit jabber timer expired.

late collision

Number of late collisions. Late collision happens when a collision occurs after transmitting the preamble. The most common cause of late collisions is that your Ethernet cable segments are too long for the speed at which you are transmitting.

deferred

Indicates that the chip had to defer while ready to transmit a frame because the carrier was asserted.

lost carrier

Number of times the carrier was lost during transmission.

no carrier

Number of times the carrier was not present during the transmission.

PAUSE output

Not supported.

output buffer failures

Number of times that a packet was not output from the output hold queue because of a shortage of shared memory.

output buffers swapped out

Number of packets stored in main memory when the output queue is full; swapping buffers to main memory prevents packets from being dropped when output is congested. The number is high when traffic is bursty.